OBJECTIVES: 1. To identify and characterize lymphocyte cell surface determinants, especially those which mark functional lymphocyte subpopulations; and to functionally characterize lymphocyte subpopulations carrying different surface markers. 2. To genetically map loci controlling lymphocyte surface determinants. 3. To fuse myeloma cells with normal antibody-producing cells, in order to obtain B cell hybrid culture lines which secrete large quantities of antibodies of interest or utility. 3. To study the genetics, immune mechanisms and relationships between the occurrence of reticulum cell sarcomas and abnormalities in regulation of the immune response in SJL/J mice.